+Def/-Atk Ninian any good?

She's not meant for combat anyway, the only damage she'll be doing is against red heroes with Triangle Adept equipped as her A passive and it's only if she's needed to do damage. Otherwise she's best kept out of harms way and gives up her turn for another ally's. Those IVs are good since her attack is nonexistent and +def helps TA scale better to make her bulkier against physical reds.

Is it a Ninian? Then it's good!

No, but seriously - I really like that IV for her. I have a +Res/-Def and would absolutely love to have a version that could take melee hits more effectively. Atk bane is really not a big deal, especially if you plan to run her as a Dance/Buff Bot.